High efficiency galvanic isolation is needed in many power electronic applications. Transformer based isolation may be needed due to safety, change of voltage levels, or functional issues. Some renewable energy sources need galvanic isolation to work properly; among them are different types of thin film solar panels.
A solar cell panel generates DC power. To supply the DC power to an AC load, either directly or via an AC power distribution network, a power converter system must be connected between the solar cell panel and the AC load for converting the DC power to AC power. Such power converter systems normally comprise a DC/DC converter and a DC/AC converter, the DC/AC converter normally being referred to as an inverter. In addition, the system comprises a control system for controlling the converters, and other components such as filters, fuses, cooling systems etc.
The DC output power generated by a solar cell panel is changing with sun intensity and temperature. High conversion efficiency is very important to maximize energy harvest from a solar plant in the context of making the investment profitable.
The series resonant LLC DC/DC converter has become a popular alternative to PWM type converters in many applications. One advantage with the resonant converter is that it can be designed for high efficiency for all load and input/output voltage conditions since it can maintain zero-voltage switching for all operating conditions.
The practical limitation for a single resonant LLC converter is set by the increasing size and cost of the resonant inductor as the output power increases. Therefore, high power DC/DC-converters are provided as many smaller series resonant LLC converters in parallel, which increase the cost considerably due to the number of components.
The object of the present invention is to provide a resonant circuit with high efficiency and low cost, and which has high efficiency for a wide input voltage range. Moreover, the object is to reduce the number of components, and thereby reducing the complexity and costs involved. In addition, it is an object of the invention to reduce the ripple currents generated by the converter.
The object of the invention is also to provide a resonant DC/DC converter with such a resonant circuit.